The present invention relates to the field of optical correlators, and more specifically to phase-only filters for use in optical correlators.
Previous work has shown that phase-only (POF) and binary phase-only (BPOF) optical filters have much larger, sharper correlation peaks than classically matched filters; see J. L. Horner and P. D. Gianino, "Phase-only Matched Filtering", Appl. Opt. 23, 812 (1984) and J. L. Horner and J. R. Leger, "Pattern Recognition with Binary Phase-only Filters", Appl. Opt. 24, 609 (1985). In addition, phase-only filters have 100% light throughput and when implemented on an electrically addressed spatial light modulator (SLM) in a real-time system, require approximately 1/25 of the memory storage space of a holographic matched filter. Up until now the BPOF, also described and claimed in my U.S. Pat. No. 4,765,714 incorporated by reference, had to be implemented on a phase-modulating SLM.
It is an object of the present invention to provide a novel and simple method which allows phase-only filters to be written on an amplitude modulating device, as most SLMs are, photographic film, or a VLSI photomask. For example, this allows a researcher who doesn't own the more expensive phase-only SLM to implement a POF or BPOF. He or she can generate the filter on a PC, then photograph the output CRT screen or use an inexpensive liquid crystal television.